U.S. Pat. No. 4,063,220, which issued Dec. 13, 1977, entitled "Multipoint Data Communication System With Collision Detection", discloses a bit serial receiver transceiver network continuously connected to a plurality of communicating devices. Such is accomplished by forming the network of any one of a plurality of transmitting media, such as coaxial cable, optical fiber or other, connected together into one branched network by constantly active devices, like repeaters, by which communications necessarily adapted to one medium are translated into another medium. The patent further goes on to state that distributed along the communicating cable network are a plurality of stations, each including a using device generally categorized as either a computer, an auxiliary memory, or an input/output terminal. Each using host device, whether it be a computer or a remote terminal, is tied to the coaxial cable by way of a T-connector, or tap, connecting to a transceiver in series with an interface stage which in turn connects to the using device.
Three signals (transmit, receive, and collision) and power are transferred through the cable which connects the host equipment with the transceiver module. Host generated transmit signals are transferred to the transceiver. Transceiver generated receive and collision signals are transferred to the host equipment. Power for energizing the transceiver circuitry is transferred from the host source.
The system described is generally now publicly known as an Ethernet connection which, as set forth above, employs a drop cable between the transceiver module and the user host equipment. The transceiver module is attached to the Ethernet coaxial cable. User host equipment is a terminal, personal computer, workstation, printer, file server, gateway, etc.
IEEE specification 802.3 contains an industry accepted definition of the drop cable. Attention is drawn to FIG. 1 of the present application. This cable has five twisted pairs, with individual pair shields and an overall shield. One pair is used for each of the three signals and another for power. The fifth pair is user defined. Each twisted pair has a characteristic impedance of 78 ohms. Cable connections are through 15 pin sub-miniature "D" connectors, male to host and female to transceiver. Each pair shield has a specific pin assignment. The overall shield is connected through the conductive connector housing.
Transmit and receive signals are Manchester encoded data at a 10 megabit per second data rate. Transmit and receive waveforms have fundamental frequencies of 10 Mhz with continuous "1" or "0" data patterns or 5 Mhz with alternate "1"/"0" data patterns. A collision signal is a burst of 10 Mhz square wave. All three signals are essentially switching waveforms with controlled rise and fall times. Power is from an 11.4 to 15.75 volt DC supply within the host station.
According to the present invention, the proposed cable herein has only two twisted, jointly shielded pairs to convey the three signals (transmit, receive, and collision) and power. AC differences in the pairs constitute the third signal channel. DC difference in the pairs provides the power source for transceiver operation. Using standard 9 pin subminiature "D" connectors and lower cost cable, the cable assembly is less expensive than the IEEE standard drop cable.